The present invention relates to a method for verifying a torque estimation of an engine. The inventive method is adapted for engines having an auxiliary brake. Thus, the method is well suited for the use in heavy vehicles.
In modern heavy vehicles, such as trucks, tractors, busses and other commercial vehicles, several systems for estimating and controlling the driving parameters of the engine and of the vehicle are known. These often relates to compensating the driving parameters of the engine and the braking parameters for the brake systems. Depending on the available sensors on the vehicle, some parameters can be measured directly by the sensors, and other parameters must be estimated by using the available measurements.
Some vehicles, e.g. the ones equipped with air suspension, have the capability to measure the weight of the load of the vehicle directly by using the air suspension pressure sensors. The total weight of the vehicle can thus easily be obtained since the unloaded weight of the vehicle is known. Other vehicles, e.g. such that have conventional leaf springs, are usually not provided with sensors that can measure the weight of the load directly. Instead, different ways of obtaining the weight of the vehicle are known.
In one method, an estimate of the weight of a vehicle is calculated from a measured acceleration and an estimated or measured engine torque. The engine torque can be measured by a torque sensor positioned e.g. on the gearbox input shaft. An estimate for the engine torque may be based on the amount of fuel injected into the engine. The amount of injected fuel is input in a fuel injection table which will output an estimate for the engine torque at any given time. In this way, an estimate for the weight of the vehicle or the vehicle combination can be provided.
In order to be able to set weight dependent control parameters of the vehicle, it is important that the estimated weight of the vehicle is as precise as possible. If the estimated weight is lower than the actual weight, the vehicle may be overloaded when an additional load is loaded on the vehicle. It is also possible that the brakes are applied with a too low brake pressure which may lead to a longer brake distance. If the estimated weight is higher than the actual weight, the fuel consumption may be higher than necessary and the vehicle may not be operated as economical as possible. For a vehicle that is not provided with an engine torque sensor, it is thus important that the engine torque is estimated properly.
U.S. Pat. No. 6,144,928 describes a method for determining the weight of a vehicle, in particular for a commercial vehicle having a towing vehicle and a trailer/semitrailer. By the method, it is possible to determine the mass distribution relation between the complete vehicle combination and the towing vehicle alone. This will allow for a proper distribution of the brake torque to individual wheel brakes, and between the towing vehicle and the trailer.
U.S. Pat. No. 6,144,928 describes a method for determining the mass of a vehicle with at least two measurements offset in time within a measuring period, where one measurement is performed during a traction-free phase and the other measurement is performed during a traction phase. One measurement is preferably performed within the traction-free phase during a gearshift and the other during a traction phase before or after the gearshift.
US2010/00049415 describes a method for compensating a vehicle brake value based on the mass of the vehicle.
In these and other methods, the weight of the vehicle is estimated in different ways. There is however still room for improvements.
It is desirable to provide a method for verifying an engine torque estimation. It is also desirable to provide a method for detecting manipulated engine control parameters. It is also desirable to provide a method for detecting a non-approved engine modification. It is also desirable to provide a method for ensuring that the vehicle can be driven safely after a non-approved modification is detected.
In a method for verifying an engine torque estimation, comprising the steps of estimating the engine torque based on the amount of fuel injected into the engine, where the engine torque is obtained from a fuel injection table and estimating a first vehicle weight value by a calculation based on the acceleration of the vehicle and the estimated engine torque, an auxiliary brake torque is estimated by using an auxiliary brake table, a second vehicle weight value is estimated by a calculation based on the estimated auxiliary brake torque, and in that the first vehicle weight value is compared with the second vehicle weight value.
By this first embodiment of the method for verifying an engine torque estimation according to the invention, it is possible to detect if the actual engine torque of a vehicle deviates from the original engine torque of that vehicle. This is done without using a specific separate torque sensor. The advantage of this is that a manipulation of the control parameters for the engine in the engine control system can be detected. Such manipulation can lead to excess wear of the engine, to overload of the engine or engine components and/or to excessive temperatures of the engine or engine components. Further, when the estimated engine torque is used to calculate the weight of the vehicle, the calculated weight ma be erroneous which in turn may affect the weight dependent parameters of the vehicle.
In an advantageous development of the inventive method, the auxiliary brake is an engine brake and the auxiliary brake table uses the engine speed as input. In this way, the engine torque can be obtained in an easy way and there is no need for a retarder or the like.
In an advantageous development of the inventive method, a message is provided which contains the difference between the first vehicle weight value and the second vehicle weight value. In this way, the result can be presented in an easy way. Such a message may be given to the driver of the vehicle or may be sent to a stationary control station. The message may also be stored in a memory for further use. p In an advantageous development of the invention, the first vehicle weight values and the second vehicle weight values are stored in a table within predefined time intervals. In this way, it is possible to obtain a long term history for the vehicle. This makes it possible to detect if a vehicle is driven with manipulated engine parameters at some periods and with the regular engine parameters when maintenance is due. It may also be possible to detect if a different fuel has been used at some time periods.